The present invention is generally directed to a porous membrane. In particular, the present invention is directed to a porous expanded polytetrafluoroethylene membrane having improved properties and made from multiple extrudates.
Membranes made from expanded polytetrafluoroethylene (ePTFE) are known. Such known membranes are used in many applications because of their chemical inertness. Exemplary applications for ePTFE membrane use include waterproof and breathable garments, fluid filtration, medical implantation and venting.
The membranes are typically made to attain a particular property such as air permeability or moisture vapor transmission. The desired property can often be attained by producing a membrane with a predetermined pore size, thickness and/or unit weight. Previous attempts at improving membrane properties have been to coat the membrane with a polymer such as polyurethane or to use multiple membranes or intermediate membrane components to provide a composite membrane. Despite this ability to modify the ultimate resultant membrane, there is still a need to improve the membrane.